This invention relates in general to electronic xe2x80x9cbackplanes,xe2x80x9d as defined below, used in computers, and in particular to a backplane which can be assembled and selectively configured from interconnected printed circuit board modules.
As used herein the term xe2x80x9cbackplanexe2x80x9d in general refers to one or more open-architecture computer signal buses traversing a planar medium and communicating with a plurality of circuit board connectors affixed to the medium.
This invention is very advantageous in the field of microprocessor based computers specially designed for use in industrial applications and mission-critical environments, such as computers designed according to the PICMG (PCI Industrial Computer Manufacturers Group) specification for industrial PCI/ISA passive backplanes. These computers generally have a passive I/O (input/output) backplane into which are plugged a microprocessor (either mounted on a single-board computer circuit card, i.e. a xe2x80x9cCPU cardxe2x80x9d, or not), and a variety of add-on circuit cards for communication via the bus(es) with the microprocessor. (Throughout this document PCI and ISA refer respectively to the well known Peripheral Component Interconnect and Industry Standard Adapter standards for personal computer I/O buses.)
The development of PICMG computers based on passive backplane technology has been driven by the needs of the industrial and Computer-Telephony Integration (CTI) markets. Personal computers designed for desktop use are based on motherboard architectures which fail to address a number of important requirements for industrial and CTI use. For example, a motherboard structure is inflexible and may require the replacement of the entire motherboard in order to repair or to upgrade the system. This results in long system downtime which may be tolerable in a system used for office applications, but which is totally unacceptable in a system which controls the core processes on which a manufacturing business depends.
Also, many industrial and CTI applications require a large number of expansion slots for real-world I/O or speech cards. These are not available on motherboard-based computers. Additionally, the overall construction of the motherboard and I/O expansion board system is not designed to cope with the harsh environmental demands of many industrial applications.
A passive backplane architecture solves these problems by completely dispensing with the motherboard. In a passive backplane computer, a system bus is used to couple a plug-in microprocessor with a plurality of plug-in add-on cards. This architecture makes rapid repair by card substitution possible, and system upgrades and changes are greatly simplified, with minimum system downtime.
Because of the advantages of a passive backplane and a plug-in processor, and because there was no configuration standard for PCI buses, a group of industrial computer product vendors, with a long history of developing PC architecture products for industrial use joined forces, and in 1994 they established the PCI Industrial Computer Manufacturers Group (PICMG) with the mission to define an industrial PCI/ISA passive backplane and CPU card interface specification. The result was a comprehensive specification for a passive backplane architecture to support both PCI and ISA I/O buses, the PCI/ISA industrial standard.
Conventionally a PICMG backplane is oriented horizontally, i.e. face up, in a rack-mounted frame and a CPU card plugs vertically into the backplane. When plugged-in, the CPU card is coupled to a plurality of additional ISA and PCI connectors, via the backplane, for communicating with add-on cards. However conventionally the backplane is a single printed circuit board and the number of connectors on it are fixed and thus the expandability of the computer is limited. If a user has filled all the connectors, the user cannot install anymore add-on cards. Also, conventional backplanes have a fixed mix of ISA, PCI and other types of connectors. This further limits the expandability of the computer. If a user has used all the ISA connectors, for example, and wants to add another ISA card, the user must replace the entire backplane with one having a mix of connectors to match the user""s needs. Also, a supplier of such computers must make a variety of backplanes available to customers to satisfy their varying requirements.
This invention solves these problems by providing a computer builder with the means to custom assemble backplanes from a relatively small set of modules. The builder can tailor a backplane for a customer. A builder can vary the footprint of the backplane, the mix of connectors, and can even expand a customer""s system by retrofit if the customer""s system has a preexisting backplane according to this invention.
Other advantages and attributes of this invention will be readily discernable upon a reading of the text hereinafter.
An object of this invention is to provide a computer backplane comprising an assemblage of interconnected printed circuit boards in a coplanar arrangement.
A further object of this invention is to provide a set of selectable backplane modules from which a backplane can be assembled.
A further object of this invention is to provide a backplane as described above which can be re-configured in the field.
A further object of this invention is to provide a PICMG passive backplane customizable according to a customer""s needs.
These objects, and other objects expressed or implied in this document, are accomplished by a modular backplane having a first module comprising: (1) a first circuit board, (2) an orthogonally oriented connector mounted on the first circuit board for coupling an open input/output bus from a central processing unit to the first circuit board, and (3) an edge oriented connector disposed along an edge of the first circuit board, said connector communicating with the input/output bus via the first circuit board; a second module comprising: (1) a second circuit board, (2) a first edge oriented connector disposed along an edge of the second circuit board for coplanarly coupling with the edge oriented connector of the first circuit board to communicate the input/output bus to the second circuit board, and (3) a plurality of orthogonally oriented connectors affixed to the second circuit board and communicating with the input/output bus via the second circuit board; and a base for mechanically supporting the first and second modules in a coupled, coplanar relationship. Preferably the backplane further has a second edge oriented connector disposed along an opposite edge of the second circuit board, the second edge oriented connector communicating with the input/output bus vis the second circuit board, a third module comprising: (1) a third circuit board; (2) a first edge oriented connector disposed along an edge of the third circuit board for coplanarly coupling with the second edge oriented connector of the second circuit board to communicate the input/output bus to the third circuit board; (3) a plurality of orthogonally oriented connectors affixed to the third circuit board and communicating with the input/output bus via the third circuit board; and (4) the base providing support for all three modules in a coupled, coplanar relationship. An embodiment of this invention has a set of modules from which custom passive backplanes can be assembled. The modules coplanarly couple together and are mounted on a rigid base plate which holds them coupled and coplanar. Each module has a plurality of orthogonally oriented card connectors. Preferably there is a CPU module into which is plugged a CPU card from which an ISA bus and a PCI bus originates. On one edge of the CPU module is an connector communicating with the ISA bus. This connector is for chaining together one or more ISA modules, each of which expands the ISA bus to three more ISA connectors. On an opposite edge of the CPU module is an connector communicating with the PCI bus. This connector is for chaining together one or more PCI modules, either 32-bit or 64-bit, each of which expands the PCI bus to three more PCI connectors. Power and ground can be jumpered from module to module or can be directly connected to any module.